In recent years in view of the preservation of global environment, biodegradable polymers that can be degraded in natural environment thanks to the actions of the microbes existing in the earth and water attract attention, and various biodegradable polymers are developed. Among them, for example, polyhydroxy butyrate, polycaprolactone, aliphatic polyesters obtained from an aliphatic dicarboxylic acid such as succinic acid or adipic acid and a glycol such as ethylene glycol or butanediol, polylactic acid resin, etc. are well known as biodegradable polymers that can be melt-molded. Among them, polylactic acid resin is expected as a melt-moldable biopolymer for such reasons that lactic acid as the monomer can be produced at a low cost using biomass such as corn as the raw material by a fermentation method using a microbe and that the polylactic acid resin is transparent and has a melting point as high as about 170° C.
However, since the glass transition temperature of polylactic acid resin is about 60° C., the resin is likely to be thermally deformed or declines greatly in stiffness at about this temperature. So, it has such a problem that in the case where it is used as various molded articles, it is likely to be thermally deformed and is difficult to use under ordinary conditions of use. A polylactic acid-based material with excellent heat resistance is being demanded.
Further, in the case where an injection molded article is produced, it is important that the resin has excellent flowability in view of moldability in the injection molding step. So, a polylactic acid-based material excellent in all of transparency, heat resistance and flowability is being demanded.
Furthermore, polylactic acid resin has a further other problem that since it is fragile and low in impact resistance, various molded articles produced by using the resin are likely to be cracked or broken in any other way and are difficult to use. So, a polylactic acid-based material with excellent impact resistance is being demanded.
Patent document 1 relates to a resin composition consisting of polylactic acid and an acrylate polymer, and describes that a resin composition with excellent heat resistance can be obtained. However, the document does not disclose anything about sustaining the transparency of polylactic acid at all, and even the examples of the document do not refer to the transparency or flowability, though they refer to higher heat resistance. The document does not suggest a solving means for obtaining a resin composition excellent in all of transparency, heat resistance and flowability at all.
Patent document 2 relates to a resin composition consisting of any of α-hydroxycarboxylic acid polymers including polylactic acid and a poly(meth)acrylate, and describes that a resin composition with excellent hydrolyzability can be obtained. Patent document 3 relates to a resin composition consisting of polylactic acid and an acrylic compound, and describes that a resin composition with excellent moldability can be obtained. However, neither of the documents discloses heat resistance or flowability at all, and suggests a solving means for obtaining a resin composition excellent in all of transparency, heat resistance and flowability at all.
Patent document 4 relates to a resin composition consisting of a polylactic acid-based polymer and an acrylic polymer and describes that a resin composition excellent in both transparency and heat resistance can be obtained. Patent document 5 relates to a resin composition consisting of polylactic acid and a poly (meth)acrylate and describes that a biaxially oriented film formed of a resin composition excellent in both transparency and heat resistance can be obtained. Patent document 6 relates to a resin composition consisting of polylactic acid and polymethyl methacrylate and describes that a resin composition excellent in both transparency and heat resistance can be obtained. Non-patent documents 1 and 2 respectively describe that if polylactic acid and polymethyl methacrylate are mixed, the glass transition temperature can be enhanced. However, the non-patent documents do not disclose anything about flowability at all and the techniques described in these documents are not sufficient in the effect of enhancing heat resistance. That is, higher heat resistance is necessary. These documents do not suggest a solving means for obtaining a resin composition excellent in all of transparency, heat resistance and flowability at all.
Patent document 7 describes that a resin composition consisting of a (meth)acrylic acid ester-based polymer and a rubbery polymer can provide a resin composition excellent in all of transparency, heat resistance and impact resistance. However, the document does not disclose the mixing of a polylactic acid-based resin at all, and does not suggest at all a solving means for providing a resin composition containing a polylactic acid-based resin, which is excellent in all of transparency, heat resistance, flowability and impact resistance.    [Patent document 1] U.S. Pat. No. 5,300,576 (pages 1-2)    [Patent document 2] JP8-59949A (pages 1 to 2)    [Patent document 3] JP2002-155207A (pages 1 to 2)    [Patent document 4] JP2004-269720A (pages 1 to 2)    [Patent document 5] WO2004/87812 (pages 1 to 3)    [Patent document 6] JP2005-171204A (pages 1 to 2)    [Patent document 7] JP2003-26891A (pages 1 to 2)    [Non-patent document 1] Polymer Preprints Japan, 42 (3), 1180 (1993)    [Non-patent document 2] Polymer, 39 (26), 6891 (1998)